Multilayer structure superior in gas barrier property

ABSTRACT

A multi-layer structure with a gas barrier layer of which the oxygen permeation coefficient under a wet and heated condition is suppressed to be of a low value while maintaining excellent workability and mechanical strength. The multi-layer structure has a gas barrier layer with excellent gas barrier property, the gas barrier layer comprising a resin composition obtained by blending a thermoplastic resin having an oxygen permeation coefficient at 20° C. and 0% RH of not larger than 10 −12  cc·cm/cm 2 /sec/cmHg with a transition metal catalyst and an oxidizing organic component, said oxidizing organic component having an average diameter of dispersed particles of not larger than 1 μm as found by an area method in cross section of said gas barrier layer in the direction of thickness thereof, and an area ratio occupied by the dispersed particles being not smaller than 1% in cross section of said gas barrier layer in the direction of thickness thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multi-layer structure equipped with agas barrier member having excellent resistance against wet heatedconditions and, particularly, excellent oxygen-blocking property underhighly humid conditions.

2. Description of the Related Art

As packaging containers, there have heretofore been used metal cans,glass bottles and a variety of plastic containers accompanied, however,by such problems as degeneration of the content and drop of flavor dueto oxygen remaining in the container or due to oxygen that enterspermeating through the container walls.

In the case of the metal cans and glass bottles, no oxygen permeatesthrough the container walls and a problem stems from only oxygenremaining in the container. In the case of the plastic containers, onthe other hand, oxygen permeates through the container walls to a degreethat is no longer negligible arousing a problem from the standpoint ofpreserving the content.

To prevent this problem, the container wall is formed in a multi-layerstructure in the case of the plastic containers, and at least one layeramong them is formed of a resin having oxygen-blocking property, such asan ethylene/vinyl alcohol copolymer.

In order to remove oxygen in the container, a deoxidizing agent has longbeen used. An example of using the deoxidizing agent in the containerwall has been taught in Japanese Examined Patent Publication (Kokoku)No. 1824/1987 according to which a multi-layer structure for packagingis obtained by laminating a layer having an oxygen gas shut-off propertyon a layer formed by blending an oxygen-permeable resin with adeoxidizing agent comprising chiefly a reducing material such as ironpowder.

Japanese Unexamined Patent Publication No. 278344/1989 proposed by thepresent inventors discloses a plastic multi-layer container of alaminated structure comprising layers of a humidity-resistantthermoplastic resin provided on both sides of an intermediate layer of aresin composition obtained by blending a gas-barrier thermoplastic resinhaving an oxygen permeation coefficient at 20° C. and 0% RH of notlarger than 10⁻¹² cc·cm/cm²/sec/cmHg and a water-absorbing amount at 20°C. and 100% RH of not smaller than 0.5% with an organic metal complex ofa transition metal.

International Patent Publication No. 500846/1990 discloses a barrierwall for wrapping containing a composition of a polymer havingoxygen-trapping property or containing a layer of the above composition,the composition trapping oxygen by catalytically oxidizing theoxidizable organic components with a metal catalyst. As the oxidizableorganic components, there have been disclosed a polyamide and,particularly, a xylylene group-containing polyamide.

A resin having excellent gas barrier property, such as an ethylene/vinylalcohol copolymer (EVOH) exhibits very excellent oxygen shut-offproperty under low-humidity conditions accompanied, however, by such aproblem that oxygen permeability becomes very great under high-humidityconditions.

In order to improve the content-preserving property, on the other hand,the gas barrier resin is, in many cases, used in combination with aheat-sterilizing packaging method, such as hot-water sterilization, boilsterilization or retort sterilization. During the heat-sterilization,however, the ethylene/vinyl alcohol copolymer (EVOH) is placed underhigh-humidity conditions not only permitting oxygen to permeate throughto a large extent but also being placed in an oxygen-permeatingcondition even after the sterilization due to water-retaining propertyof the EVOH, making it difficult to obtain a desired gas barrierproperty.

The high gas barrier property possessed by the ethylene/vinyl alcoholcopolymer is due to a high degree of hydrogen coupling possessed by thiscopolymer. However, the barrier effect due to the hydrogen couplingbased on the hydroxyl group tends to be loosened under a condition wherethe water content (humidity) is acting to a high degree. This propertyis of an essential nature and cannot be easily improved.

SUMMARY OF THE INVENTION

The present inventors have discovered the fact that the oxygenpermeation coefficient of the multi-layer structure can be markedlyimproved under the wet and heated condition yet maintaining excellentworkability and mechanical strength if a gas barrier layer is formed byblending a particular gas barrier resin with a transition metal catalystand an oxidizing organic component, and if the dispersion structure andthe profile structure of the oxidizing organic component are controlledto lie within particular ranges in cross section of the gas barrierlayer in the direction of thickness.

It is therefore an object of the present invention to provide amulti-layer structure with a gas barrier layer of which the oxygenpermeation coefficient under a wet and heated condition is suppressed tobe of a low value while maintaining excellent workability and mechanicalstrength.

According to the present invention, there is provided a multi-layerstructure having a gas barrier layer with excellent gas barrierproperty, said gas barrier layer comprising a resin composition obtainedby blending a thermoplastic resin having an oxygen permeationcoefficient at 20° C. and 0% RH of not larger than 10⁻¹² cc·cm²/sec/cmHgwith a transition metal catalyst and an oxidizing organic component,said oxidizing organic component having an average diameter of dispersedparticles of not larger than 1 μm as found by an area method in crosssection of said gas barrier layer in the direction of thickness thereof,and an area ratio occupied by the dispersed particles being not smallerthan 1% in cross section of said gas barrier layer in the direction ofthickness thereof.

In the multi-layer structure of the present invention, it is desiredthat:

-   1. when the direction of thickness of said gas barrier layer is    regarded to be a short axis and a direction perpendicular to the    direction of thickness is regarded to be a long axis in cross    section of said gas barrier layer in the direction of thickness    thereof, a maximum value of an aspect ratio of dispersed particles    of said oxidizing organic component represented by the length in the    long axis direction/length in the short axis direction, is not    smaller than 2;-   2. said oxidizing organic component is a polyene polymer;-   3. said oxidizing organic component is a resin having a functional    group;-   4. said oxidizing organic component is a resin having a carboxylic    acid group or a carboxylic anhydride group; and-   5. said thermoplastic resin is an ethylene/vinyl alcohol copolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph plotting a relationship between the days that havepassed and an increase (%) in the amount of oxygen in the container whena bottle having a multi-layer structure of propylene/gas barrier layer(20 to 25 μm thick)/polypropylene is boiled and is, then, aged at 30° C.(100% RH inside the bottle and 80% RH outside the bottle);

FIG. 2 is a scanning-type electron microphotograph of a gas barrierlayer having dispersion and profile structures in cross section in thedirection of thickness according to the present invention, thecontinuous phase being an ethylene/vinyl alcohol copolymer and thedispersion phase being a maleic acid-modified polybutadiene;

FIG. 3 is a scanning-type electron microphotograph of another gasbarrier layer having dispersion and profile structures in cross sectionin the direction of thickness falling outside the scope of the presentinvention, the continuous phase being an ethylene/vinyl alcoholcopolymer and the dispersion phase being a polybutadiene;

FIG. 4 is a scanning-type electron microphotograph of a further gasbarrier layer having dispersion and profile structures in cross sectionin the direction of thickness falling outside the scope of the presentinvention, the continuous phase being an ethylene/vinyl alcoholcopolymer and the dispersion phase being an OH-modified polyisoprene;and

FIG. 5 is a diagram illustrating the gas barrier layer of the presentinvention in cross section in the direction of thickness.

EMBODIMENTS OF THE INVENTION

[Action]

A multi-layer structure having a gas barrier layer of the presentinvention has a feature in that a gas barrier layer is formed of a resincomposition obtained by selecting a thermoplastic resin having an oxygenpermeation coefficient at 20° C. and 0% RH of not larger than 10⁻¹²cc·cm/cm²/sec/cmHg as a base resin and blending it with a transitionmetal catalyst and an oxidizing organic component, and that thedispersion structure and the profile structure of the oxidizing organiccomponent are controlled to lie within particular ranges in crosssection of the gas barrier layer in the direction of thickness thereof.

The thermoplastic resin used in the present invention serves as a chiefcomponent, i.e., serves as a matrix of the gas barrier resincomposition. The thermoplastic resin having an oxygen permeationcoefficient within the above-mentioned range exhibits excellent gasshut-off property.

The invention further uses an oxidizing organic component. The oxidizingorganic component exhibits the action of absorbing oxygen as it isoxidized by the action of a transition metal catalyst that will bedescribed later.

It is considered that the oxidizing organic component easily pulls out ahydrogen atom at a position of an active carbon atom in the resin tothereby generate a radical. The composition containing the transitionmetal catalyst and the oxidizing organic component absorbs oxygenthrough the oxidation of the organic component, as a matter of course.It is believed that the oxidation occurs through the reactions, i.e.,(1) generation of radicals as the hydrogen atoms are pulled out from thecarbon atoms by the transition metal catalyst, (2) generation of peroxyradicals as oxygen molecules are added to the radicals, and (3) pullingout of hydrogen atoms by peroxy radicals.

In the gas barrier resin composition used in the present invention asdescribed above, the gas barrier thermoplastic resin plays the role ofshutting off the gas without being substantially oxidized. The oxidizingorganic component, on the other hand, plays the role of absorbing oxygenby oxidation. Thus, the gas shut-off property and the oxygen absorbingproperty are exhibited as separate functions creating a distinguishedfeature.

As described already, if once put to the wet and heated condition, thegas barrier resin such as ethylene/vinyl alcohol copolymer loses the gasbarrier property to a large extent. On the other hand, the gas barrierlayer having a fine dispersion structure and a multi-layer profilestructure obtained by blending the ethylene/vinyl alcohol copolymer witha transition metal catalyst and an oxidizing organic component, exhibitsan unexpected effect of maintaining the oxygen permeation coefficient onan excellent level even after having been put to the wet and heatedcondition.

FIG. 1 in the attached drawing is a graph plotting a relationshipbetween the days that have passed and an increase (%) in the amount ofoxygen in the container when a bottle having a multi-layer structure ofpropylene/gas barrier layer (20 to 25 μm thick)/polypropylene is boiledand is, then, aged at 30° C. (100% RH inside the bottle and 80% RHoutside the bottle).

The above result tells that in the bottle using the ethylene/vinylalcohol copolymer as the gas barrier layer, the oxygen concentrationsharply increases right after the boiling and, further, continues toincrease with the passage of time. In the bottle forming the finedispersion structure and the multi-layer profile structure by blendingthe ethylene/vinyl alcohol copolymer with a transition metal catalystand an oxidizing organic component, on the other hand, an increase inthe oxygen concentration right after the boiling is suppressed and asubsequent increase in the oxygen concentration with the passage of timeis suppressed, too, manifesting unexpected action and effect of thepresent invention.

In the dispersion structure in which the gas barrier thermoplastic resinis existing as a continues phase (matrix) and the oxidizing organiccomponent is existing as a dispersion phase, in particular, the surfaceareas of the oxidizing organic component which is the dispersion phaseis increasing, whereby oxygen is efficiently absorbed. Even after theoxidation of the dispersion layer has proceeded, the gas barrierthermoplastic resin remains as a continuous phase offering an advantageof maintaining excellent gas shut-off property and mechanical strength.Further, since the oxidizing organic component is covered with thecontinuous phase of gas barrier thermoplastic resin, there is obtainedsuch an advantage of excellent hygienic property.

The dispersion and profile structures of the oxidizing organic componentin the gas barrier layer can be quantitatively treated by finding anaverage particle diameter of dispersed particles by the area method incross section of the gas barrier method in the direction of thicknessand by finding the area ratio occupied by the dispersed particles incross section of the gas barrier layer in the direction of thickness.

Referring to FIG. 5, the cross section of the gas barrier layer in thedirection of thickness according to the present invention may be eithera cross section (direction of arrow A) in a direction perpendicular tothe direction of height thereof or a cross section (direction of arrowB) in a direction in parallel therewith provided the multi-layerstructure is a barrel portion of a container of the shape of bottle.

When the multi-layer structure is a sheet or a film, the cross sectionmay be either the one in a direction perpendicular to the direction ofwinding or the one in parallel therewith.

When the gas barrier layer is stretched, the diameters of the dispersedparticles and the area occupied by the dispersed particle differdepending upon a direction in parallel with the direction of stretch ora direction perpendicular thereto. According to the present invention,however, excellent barrier property and mechanical strength aremaintained if the average diameter of the dispersed particles of theoxidizing polymer is not larger than 1 μm in either one cross sectionwhich is in parallel with the direction of stretch or is perpendicularthereto and if the area ratio occupied by the dispersed particles is notsmaller than 1% in cross section of the gas barrier layer in thedirection of thickness.

The oxidizing organic component contained as a dispersion phase in thegas barrier layer can be dyed by using a dye capable of selectivelydying the oxidizing organic component only in cross section of the gasbarrier layer.

The cross section of the gas barrier layer after dyed is photographed byusing a scanning-type electron microscope (SEM), the picture of the SEMphotograph is read by a scanner, the oxidizing organic component andother portions are discriminated from one another on a PC screen byusing a picture processing software, thereby to measure the number n ofdispersed particles and the area S of the dispersed oxidizing organiccomponent particles present on a predetermined area S_(o). Thisoperation is conducted for a plurality of visual fields to enhance theprecision, ΣS and Σn are calculated from S and n found from the visualfields, and an area average particle diameter d is found from thefollowing formula (1),d=(ΣS/Σn)^(1/2)  (1)

Further, in compliance with the following formula (2), an area ratio αoccupied by the dispersed particles is found from the above S_(o) and Sthat have been found for the plurality of visual fields,α=100×ΣS/ΣS _(o)  (2)

FIG. 2 in the accompanying drawing is a scanning-type electronmicrophotograph of a gas barrier layer having dispersion and profilestructures in cross section in the direction of thickness according tothe present invention, the continuous phase being an ethylene/vinylalcohol copolymer and the dispersion phase being a maleicanhydride-modified polybutadiene.

FIG. 3 is a scanning-type electron microphotograph of another gasbarrier layer having dispersion and profile structures in cross sectionin the direction of thickness falling outside the scope of the presentinvention, the continuous phase being an ethylene/vinyl alcoholcopolymer and the dispersion phase being a polybutadiene.

FIG. 4 is a scanning-type electron microphotograph of a further gasbarrier layer having dispersion and profile structures in cross sectionin the direction of thickness falling outside the scope of the presentinvention, the continuous phase being an ethylene/vinyl alcoholcopolymer and the dispersion phase being an OH-modified polyisoprene.

Referring to these scanning-type electron microphotograph, an unexpectedfact becomes obvious in that the present invention is accomplishingdispersed particles of exceptionally fine sizes.

In the present invention, the average diameter of dispersed particles ofthe oxidizing organic component as found by an area method is selectedto be not larger than 1 μm in cross section of the gas barrier layer inthe direction of thickness thereof, and an area ratio occupied by thedispersed particles is selected to be not smaller than 1% in crosssection of the gas barrier layer in the direction of thickness thereof,making it possible to suppress the oxygen permeation amount to a smallvalue under high-temperature and wet conditions.

A multi-layer structure having the above dispersion and profilestructures can be favorably molded, enables the molded structure topossess homogeneous texture and homogeneous appearance, featuringuniform thickness and excellent smoothness.

Further, since the oxidizing organic component is present in thedispersion structure, the crystallinity of the gas barrier resin itselfand the intermolecular cohesive force are adversely affected little ascompared to when the oxidizing organic component is existing in the formof molecules. Even after the oxidizing organic component has lost theactivity, the gas barrier resin itself maintains barrier property.

Any known method can be used for controlling the dispersion structure,such as a method of finely dispersing the oxidizing organic component byusing a compatibility-imparting agent, or a method which imparts aparticular functional group to the oxidizing organic material itself sothat the oxidizing organic component is finely dispersed. In effect, theoxidizing organic component is controlled to possess the dispersionstructure to exhibit excellent gas barrier property.

In the multi-layer structure of the present invention, when thedirection of thickness of the gas barrier layer is regarded to be ashort axis and a direction perpendicular to the direction of thicknessis regarded to be a long axis in cross section of the gas barrier layerin the direction of thickness thereof, a maximum value of an aspectratio of dispersed particles of the oxidizing organic componentrepresented by the length in the long axis direction/length in the shortaxis direction, is selected to be not smaller than 2, in order tosuppress the amount of oxygen permeation down to a lower level underhigh-temperature and wet conditions.

To measure the aspect ratio, the above-mentioned SEM photograph isenlarged, lines are drawn in the direction of thickness (short axisdirection) of the gas barrier layer and in the direction (long axisdirection) perpendicular thereto, the lengths of the dispersed particlesare found in the long axis direction and in the short axis direction,the aspect ratio (length in the long axis direction/length in the shortaxis direction) is found, and a maximum aspect ratio of the dispersedparticles is found.

It is desired that the oxidizing organic component used in the presentinvention contains a resin modified with a carboxylic acid or acarboxylic anhydride. The oxidizing organic component modified with thecarboxylic acid or carboxylic anhydride can be finely and homogeneouslydispersed in the gas barrier resin suppressing the amount of oxygenpermeation down to a low value and improving the thickness and surfacehomogeneity of the multi-layer structure.

The acid value of the oxidizing organic component for obtaining gooddispersion property tends to vary depending upon the number averagemolecular weight of the oxidizing organic component. As the numberaverage molecular weight increases, there is obtained good dispersionwith a small acid value. A preferred acid value may be adjusteddepending upon the number average molecular weight and is, desirably,not smaller than 5 KOHmg/g.

[Gas Barrier Thermoplastic Resin]

The present invention uses a thermoplastic resin having an oxygenpermeation coefficient at 20° C. and 0% RH of not larger than 10⁻¹²cc·cm/cm²/sec/cmHg as a base resin of the gas barrier layer.

Any thermoplastic resin can be used so far as it satisfies theabove-mentioned conditions. Particularly preferred examples includeethylene/vinyl alcohol copolymer, polyamide or copolymer thereof,barrier polyester, and combinations thereof.

In the present invention, it is desired to use an ethylene/vinyl alcoholcopolymer as a resin having particularly excellent barrier propertyagainst oxygen and flavor component. The ethylene/vinyl alcoholcopolymer may be any known one such as a saponified copolymer obtainedby saponifying an ethylene/vinyl acetate copolymer containing ethylenein an amount of from 20 to 60 mol % and, particularly, from 25 to 50 mol% such that the degree of saponification is not smaller than 96 mol %and, particularly, not smaller than 99 mol %.

The saponified ethylene/vinyl alcohol copolymer should have a molecularweight large enough for forming a film, and desirably has a viscosityof, generally, not smaller than 0.01 dL/g and, particularly, not smallerthan 0.05 dL/g in a mixed solvent of phenol and water at a weigh ratioof 85 to 15 at 30° C.

As the polyamide resin, there can be exemplified (a) an aliphatic,alicyclic or semi-aromatic polyamide derived from a dicarboxylic acidcomponent and a diamine component, (b) a polyamide derived from anaminocarboxylic acid or a lactam thereof, or a copolyamide thereof or ablend thereof.

As the dicarboxylic acid component, there can be exemplified aliphaticdicarboxylic acids having 4 to 15 carbon atoms, such as succinic acid,adipic acid, sebacic acid, decanedicarboxylic acid, undecanedicarboxylicacid and dodecanedicarboxyic acid; and aromatic dicarboxylic acids suchas terephthalic acid and isophthalic acid.

As the diamine component, there can be exemplified straight chain orbranched chain alkylene diamines having 4 to 25 and, particularly, 6 to18 carbon atoms, such as 1,6-diaminohexane, 1,8-diaminooctane,1,10-diaminodecane, and 1,12-diaminododecane; alicyclic diamines such asbis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl)methane,4,4′-diamino-3,3′-dimethyldicyclohexylmethane and, particularly,bis(4-aminocyclohexyl)methane, 1,3-bis(aminocyclohexyl)methane, and1,3-bis(aminomethyl)cyclohexane; and aroaliphatic diamines such asm-xylylenediamine and/or p-xylylenediamine.

As the aminocarboxylic acid component, there can be exemplifiedaliphatic aminocarboxylic acids such as ω-aminocaproic acid,ω-aminooctanoic acid, ω-aminoundecanoic acid, ω-aminododecanoic acid;and aroalicyclic aminocarboxylic acids such as para-aminomethylbenzoicacid and para-aminophenylacetic acid.

Among these polymides, it is desired to use a polyamide containing axylylene group. Concrete examples include homopolymers such aspolymetaxylylene adipamide, polymetaxylylene sebacamide,polymetaxylylene suberamide, polyparaxylylene pimelamide, andpolymetaxylylene azeramide; copolymers such as metaxylene/paraxylyleneadipamide copolymer, metaxylylene/paraxylylene pimeramide copolymer,metaxylylene/paraxylylene sebacamide copolymer andmetaxylylene/paraxylylene azeramide copolymer; copolymers obtained bycopolymerizing the components of these homopolymers or copolymers withaliphatic diamine such as hexamethylenediamine, alicyclic diamine suchas piperazine, aromatic diamine such as para-bis(2-aminoethyl)benzene,aromatic dicarboxylic acid such as terephthalic acid, lactam such asε-caprolactam, ω-aminocarboxylic acid such as 7-aminoheptanoic acid, orwith aromatic aminocarboxylic acid such as para-aminomethylbenzoic acid.However, there can be particularly preferably used a polyamide obtainedfrom a diamine component comprising, chiefly, m-xylylenediamine and/orp-xylylenediamine and from aliphatic dicarboxylic acid and/or aromaticdicarboxylic acid.

These xylylene group-containing polyamides exhibit superior oxygenbarrier property to other polyamide resins, and are suited foraccomplishing the object of the present invention.

In the present invention, it is desired that the polyamide resin hasterminal amino groups at a concentration of not smaller than 40 eq/10⁶ gand, more preferably, not smaller than 50 eq/10⁶ g from the standpointof suppressing the degradation of the polyamide resin due to oxidation.

There is an intimate relationship between the degradation of thepolyamide resin due to oxidation, i.e., absorption of oxygen and theconcentration of terminal amino groups of the polyamide resin. That is,when the concentration of terminal amino groups of the polyamide resinlies within the above-mentioned relatively high range, the rate ofoxygen absorption is suppressed to be almost zero or to a value close tozero. When the concentration of terminal amino groups of the polyamideresin becomes smaller than the above range, on the other hand, the rateof absorbing oxygen of the polyamide resin tends to increase.

These polyamides should have molecular weights large enough for forminga film, and, desirably, have a relative viscosity (ηrel) of not smallerthan 1.1 and, particularly, not smaller than 1.5 as measured in theconcentrated sulfuric acid at a concentration of 1.0 g/dl and at atemperature of 30° C.

As the thermoplastic resin, there can be used an aromatic dicarboxylicacid such as terephthalic acid or isophthalic acid, and a thermoplasticpolyester derived from diols such as ethylene glycol.

As the thermoplastic resin having excellent gas barrier property, therecan be used a so-called gas barrier polyester. The gas barrier polyestercontains, in a polymer chain thereof, a terephthalic acid component (T)and an isophthalic acid component (I) at a molar ratio of T:I=95:5 to5:95 and, particularly, T:I=75:25 to 25:75, and contains an ethyleneglycol component (E) and a bis(2-hydroxyethoxy)benzene component (BHEB)at a molar ratio of E:BHEB=99.999:0.001 to 2.0:98.0 and, particularly,E:BHEB=99.95:0.05 to 40:60. As the BHEB, there is preferably used a1,3-bis(2-hydroxyethoxy)benzene.

The polyester should have a molecular weight at least large enough forforming a film and, desirably, has an inherent viscosity [η] of,generally, from 0.3 to 2.8 dl/g and, particularly, from 0.4 to 1.8 dl/gas measured in a mixed solvent of phenol and tetrachloroethane at aweight ratio of 60:40 at a temperature of 30° C.

It is also allowable to use a polyester resin comprising, chiefly, apolyglycol acid, or a polyester resin obtained by blending the abovepolyester resin with a polyester resin derived from the aromaticdicarboxylic acid and diols.

[Oxidizing Organic Component]

In the present invention, the gas barrier resin is blended with atransition metal catalyst and an oxidizing organic component.

It is desired that the oxidizing organic component has active carbonatoms so as to easily pull out hydrogen. Though there is no particularlimitation, the active carbon atoms may be those carbon atomsneighboring the carbon-carbon double bond, tertiary carbon atoms coupledto a chain on the carbon side or an active methylene group.

As the oxidizing organic component, it is desired to use a polyene-typepolymer. As the polyene used for the polyene-type polymer, there can beused a polyene having 4 to 20 carbon atoms, an oligomer or a polymercontaining a unit derived from a chained or cyclic conjugated ornon-conjugated polyene.

As the monomers, there can be exemplified conjugated dienes such asbutadiene and isoprene; chained non-conjugated dienes such as1,4-hexadiene, 3-methyl-1,4-hexadiene, 4-methyl-1,4-hexadiene,5-methyl-1,4-hexadiene, 4,5-dimethyl-1,4-hexadiene and7-methyl-1,6-octadiene; cyclic non-conjugated dienes such asmethyltetrahydroindene, 5-ethylidene-2-norbornene,5-methylene-2-norbornene, 5-isopropylidene-2-norbornene,5-vinylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene anddicyclopentadiene; and triene and chloroprene such as2,3-diisopropylidene-5-norbornene,2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2 and2-norbornadiene.

These polyenes can be used in a single kind or in a combination of twoor more kinds, or can be used in the form of a homopolymer, randomcopolymer or a block copolymer in combination with other monomers.

As the monomer used in combination with the polyene, there can beexemplified α-olefins having 2 to 20 carbon atoms, such as ethylene,propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene,1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene,1-pentadecene, 1-hexadecene, 1-heptadecene, 1-nonadecene, 1-eicosene,9-methyl-1-decene, 11-methyl-1-dodecene, and 12-ethyl-1-tetradecene.There can be further used such monomers as styrene, vinyltoluene,acrylonitrile, methacrylonitrile, vinyl acetate, methyl methacrylate andethyl acrylate.

Concrete examples of the polyene-type polymer include polybutadiene(BR), polyisoprene (IR), butyl rubber (IIR), natural rubber,nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR),styrene-isoprene rubber (SIR), chloroprene rubber (CR) andethylene-propylene-diene rubber (EPDM) to which only, however, thepolyene-type polymer is in no way limited.

The carbon-carbon double bond in the polymer may be present on the mainchain in the form of a vinylene group or may be present on the sidechain in the form of a vinyl group without any particular limitation. Ineffect, the carbon-carbon double bond may be the one capable of beingoxidized. The one in the form of the vinyl group is desirable from thestandpoint of high rate of oxidation.

It is desired that the oxidizing organic component used in the presentinvention has a functional group. As the functional group, there can beexemplified carboxylic acid group, carboxylic anhydride group,carboxylic acid ester group, carboxylic acid amide group, epoxy group,hydroxyl group, amino group and carbonyl group. Among them, carboxylicacid group and carboxylic anhydride group are particularly desired fromthe standpoint of compatibility. These functional groups may be presenton the side chains or at the terminals of the resin.

When the oxidizing organic component is a polyene-type polymer, anethylenically unsaturated monomer having the above functional group isused as a monomer for introducing the functional groups.

As the monomer used for introducing the carboxylic acid group orcarboxylic anhydride group into the polyene-type polymer, there isdesirably used an unsaturated carboxylic acid or a derivative thereof.Concretely, there can be exemplified α,β-unsaturated carboxylic acidssuch as acrylic acid, methacrylic acid, maleic acid, fumaric acid,itaconic acid, citraconic acid and tetrahydrophthalic acid; unsaturatedcarboxylic acids such as bicyclo[2,2,1]hepto-2-ene-5,6-dicarboxylicacid; α,β-unsaturated carboxylic anhydrides such as maleic anhydride,itaconic anhydride, citraconic anhydride and tetrahydrophthalicanhydride; and anhydrides of unsaturated carboxylic acid, such asbicyclo[2,21]hepto-2-ene-5,6-dicarboxylic anhydride.

The polyene-type polymer modified with acid is prepared bygraft-copolymerizing the polyene-type polymer which is a base polymerwith an unsaturated carboxylic acid or a derivative thereof by knownmeans. The polyene-type polymer modified with acid, however, can furtherbe prepared by random-copolymerizing the polyene-type polymer with anunsaturated carboxylic acid or a derivative thereof.

The oxidizing organic component having the carboxylic acid or thecarboxylic anhydride group disperses well in the ethylene/vinyl alcoholcopolymer, and smoothly absorbs oxygen.

The oxidizing organic component used in the present invention is the oneobtained by modifying the polyene-type polymer with the carboxylic acidor the carboxylic anhydride. The oxidizing organic component in thestate of a liquid resin being modified with acid or acid anhydride isdesirable from the standpoint of dispersion in the gas barrier resin.

It is desired that the oxidizing organic component used in the presentinvention is capable of absorbing oxygen in an amount of not smallerthan 2×10⁻³ mol and, particularly, not smaller than 4×10⁻³ mol per gramof the oxidizing organic component at normal temperature in the presenceof a transition metal catalyst. When the oxygen absorbing ability issmaller than the above value, the gas barrier resin must be blended withthe oxidizing organic component in large amounts to develop good oxygenbarrier property. As a result, the resin composition after blendedexhibits deteriorated workability and formability.

[Transition Metal Catalyst]

Preferred examples of the transition metal catalyst used in the presentinvention include metal components of the Group VIII of periodic table,such as iron, cobalt, nickel and the like. There can be furtherexemplified metals of the Group I, such as copper, silver and the like;metals of the Group IV, such as tin, titanium, zirconium and the like;metals of the Group V, such as vanadium; metals of the Group VI, such aschromium; and metals of the Group VIII, such as manganese. Among thesemetal components, cobalt exhibits a large oxygen absorbing rate and isparticularly suited for the object of the present invention.

The transition metal catalyst is usually used in the form of aninorganic salt, an organic salt or a complex of the above transitionmetal having a low valency.

As the inorganic salt, there can be exemplified halide such as chloride,oxyacid salt of sulfur such as sulfate, oxyacid salt of nitrogen such asnitrate, phosphorus oxyacid salt such as phosphate, and silicate.

As the organic salt, on the other hand, there can be exemplifiedcarboxylate, sulfonate, and phosphonate. Among them, carboxylate issuited for the object of the present invention. Its concrete examplesinclude transition metal salts of acetic acid, propionic acid,isopropionic acid, butanoic acid, isobutanoic acid, pentanoic acid,isopentanoic acid, hexanoic acid, heptanoic acid, isoheptanoic acid,octanoic acid, 2-ethylhexanoic acid, nonanoic acid,3,5,5-trimethylhexanoic acid, decanoic aid, neodecanoic acid, undecanoicacid, lauric acid, myristic acid, palmitic acid, margaric acid, stearicacid, arachic acid, linderic acid, tsuzuic acid, petroselinic acid,oleic acid, linoleic acid, linolenic acid, arachidonic acid, formicacid, oxalic acid, sulfamic acid and naphthanic acid.

As the complex of a transition metal, there is used a complex withβ-diketone or β-keto-acid ester. As the β-diketone or β-keto-acid ester,there can be used, for example, acetylacetone, ethyl acetoacetate,1,3-cyclohexadion, methylenebis-1,3-cyclohexadion,2-benzyl-1,3-cyclohexadion, acetyltetralone, palmitoyltetralone,stearoyltetralone, benzoyltetralone, 2-acetylcyclohexanone,2-benzoylcyclohexanone, 2-acetyl-1,3-cyclohexanedion,benzoyl-p-chlorobenzoylmethane, bis(4-methylbenzoyl)methane,bis(2-hydroxybenzoyl)methane, benzoylacetone, tribenzoylmethane,diacetylbenzoylmethane, stearoylbenzoylmethane, palmitoylbenzoylmethane,lauroylbenzoylmethane, dibenzoylmethane, bis(4-chlorobenzoyl)methane,bis(methylene-3,4-dioxybenzoyl)methane, benzoylacetylphenylmethane,stearoyl(4-methoxybenzoyl)methane, butanoylacetone, distearoylmethane,acetylacetone, stearoylacetone, bis(cyclohexnoyl)methane anddipivaroylmethane.

[Resin Composition]

In the present invention, it is desired that the ethylene/vinyl alcoholcopolymer or the like is blended with the oxidizing organic component insuch an amount that the area ratio occupied by the dispersed particlesis not smaller than 1% and, particularly, not smaller than 2% in crosssection of the gas barrier layer in the direction of thickness. There isno particular limitation on the area ratio provided the gas barrierlayer has a structure in which the gas barrier resin is forming acontinuous layer and the oxidizing organic component is forming adispersion layer. From the standpoint of stability of the dispersionstructure, however, it is desired that the upper limit of the area ratiois not larger than 30% and, particularly, not larger than 20%.

In this case, further, it is desired that the amount of blending theoxidizing organic component in the resin composition is not larger than30% by weight and, particularly, not larger than 20% by weight from thestandpoint of workability and formability of the resin composition.

In this resin composition, further, it is desired that the transitionmetal catalyst is contained in an amount of from 100 to 1000 ppm and,particularly, from 200 to 500 ppm calculated as a transition metalamount per the total amount of the gas barrier resin and the oxidizingorganic component.

When the area ratio of the oxidizing organic component is smaller thanthe above-mentioned range, the oxygen barrier property becomesinsufficient as compared to when the area ratio is within the aboverange.

When the amount of the transition metal catalyst is smaller than theabove-mentioned range, further, the gas barrier property tends todecrease as compared to when the amount lies within the above range.When this amount exceeds the above range, the resin composition tends tobe deteriorated when it is formed by being kneaded, which is notdesirable.

The ethylene/vinyl alcohol copolymer can be blended with the transitionmetal catalyst and with the oxidizing organic component by a variety ofmeans. There is no particular order for the blending; i.e., the blendingcan be effected in any order.

In order to homogeneously blend the above components and to preventundesired oxidation of before the use as much as possible, however, itis generally desired that the transition metal catalyst is dissolved inan organic solvent, the solvent is mixed with a base resin such as apowdery or granular ethylene/vinyl alcohol copolymer and, as required,the mixture is dried in an inert atmosphere, since the amount of thetransition metal catalyst is smaller than that of the base resin such asthe ethylene/vinyl alcohol copolymer.

It is, on the other hand, desired that the base resin such as theethylene/vinyl alcohol copolymer carrying the above transition metalcatalyst is melt-blended with the oxidizing organic component. Thishelps prevent a side reaction or a pre-reaction of the transition metalcatalyst with the oxidizing organic component.

As the solvent for dissolving the transition metal catalyst, there canbe used alcohol solvents such as methanol, ethanol and butanol; ethersolvents such as dimethyl ether, diethyl ether, methyl ethyl ether,tetrahydrofuran and dioxane; ketone solvents such as methyl ethyl ketoneand cyclohexanone; and hydrocarbon solvents such as n-hexane andcyclohexane. Usually, the solvent is used in such an amount that theconcentration of the transition metal catalyst is from 5 to 90% byweight.

It is desired that the ethylene/vinyl alcohol copolymer which is thebase resin, oxidizing organic component and the transition metalcatalyst are mixed and are, then, preserved in a non-oxidizingatmosphere so will not to be oxidized during the stage preceding thecomposition. For this purpose, it is desired that the mixing and dryingare conducted under a reduced pressure condition or in a nitrogenstream.

The mixing and/or the drying can be conducted in a stage preceding thestep of formation by using a vent-type or dryer-equipped extruder orinjector.

In the most preferred embodiment of the invention, the base resin suchas the ethylene/vinyl alcohol copolymer smeared with the transitionmetal catalyst is melted and kneaded in advance by using a biaxialextruder having a side feed, and the oxidizing organic component is fedinto the melt-kneaded mixture so as to homogeneously knead themtogether.

The kneading system using the biaxial extruder is capable of effectingthe kneading at a low temperature and under a low pressure, making itpossible to obtain a homogeneously kneaded product while preventing theoccurrence of gel or the like.

The gas barrier layer used in the present invention can, as desired, beblended with a known activating agent though it is not usually needed.Though not limited thereto only, suitable examples of the activatingagent include polyethylene glycol, polypropylene glycol,ethylene/methacrylic acid copolymer, and polymers containing hydroxylgroups such as various ionomers and/or carboxyl groups.

The hydroxyl group-containing and/or carboxyl group-containing polymerscan be blended in an amount of not larger than 30 parts by weight and,particularly, from 0.01 to 10 parts by weight per 100 parts by weight ofthe ethylene/vinyl alcohol copolymer.

The oxygen-absorbing layer used in the present invention can be blendedwith known blending agents, such as filler, coloring agent,heat-resisting stabilizer, anti-aging stabilizer, anti-oxidant,anti-aging agent, photo stabilizer, ultraviolet ray absorber, antistaticagent, metal soap, lubricant such as wax, reforming resin and rubberaccording to known recipe.

Upon blending the lubricant, for example, the resin is more favorablypicked up by the screw. The lubricant may be a metal soap such asmagnesium stearate or calcium stearate; the one of the hydrocarbon type,such as fluidized, natural or synthetic paraffin, microwax, polyethylenewax or chlorinated polyethylene wax; the one of the fatty acid type,such as stearic acid or lauric acid; the one of the type of fatty acidmonoamide or bisamide, such as stearic acid amide, palmitic acid amide,oleic acid amide, erucic acid amide, methylenebisstearo amide, orethylenebisstearo amide; the one of the ester type, such as butylstearate, cured castor oil or ethylene glycol monostearate; or a mixedsystem thereof. A suitable amount of addition of the lubricant is from50 to 1000 ppm based on the thermoplastic resin.

After melt-blended, the resin composition of the present invention issuch that the ethylene/vinyl alcohol copolymer which is the base resinis forming a continuous phase (matrix) and the oxidizing organiccomponent is forming a dispersion phase.

[Multi-Layer Structure]

In the present invention, at least one layer of the gas barrier memberis combined, as required, with at least one layer of other resin toobtain a plastic multi-layer structure such as cup, tray, bottle,tubular container or pouch.

In general, it is desired that the gas barrier layer is formed on theinside of the container rather than on the outer surface so will not tobe exposed to the outer surface. It is further desired that the gasbarrier layer is formed on the outer side of the inner surface of thecontainer so will not to come into direct touch with the content. It isthus desired to provide the gas barrier layer as at least oneintermediate layer of the multi-layer resin container.

In the case of a container of the multi-layer constitution, the otherresin layer to be used in combination with the gas barrier layer may bea moisture-resistant resin such as olefin resin or thermoplasticpolyester resin, or any other gas barrier resin.

As the olefin resin, there can be exemplified polyethylenes (PE) such aslow density polyethylene (LDPE), middle density polyethylene (MDPE),high density polyethylene (HDPE), linear low density polyethylene(LLDPE) and linear very low density polyethylene (LVLDPE), as well aspolypropylene (PP), ethylene/propylene copolymer, polybutene-1,ethylene/butene-1 copolymer, propylene/butene-1 copolymer,ethylene/propylene/butene-1 copolymer, ethylene/vinyl acetate copolymerand tonically crosslinked olefin copolymer (ionomer) or a blend thereof.

As the thermoplastic polyester resin, there can be exemplified apolyester resin comprising chiefly polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polyethylene naphthalate (PEN),polyester resin comprising chiefly a polyglycolic acid, or acopolymerized polyester thereof, or a blend thereof.

As other examples of the barrier resin, there can be used cyclicolefin-type copolymer (COC) and, particularly, a copolymer of ethyleneand cyclic olefin and, more particularly, APEL of Mitsui Chemical Co.

Described below are suitable examples of the container laminated-layerstructure where OBR stands for a layer of the oxygen barrier resincomposition (hereinafter simply referred to as oxygen barrier layer).Which layer be formed on the inner surface side is freely selecteddepending upon the object.

-   -   Two-layer structure: PET/OBR, PE/OBR, PP/OBR.    -   Three-layer structure: PE/OBR/PET, PET/OBR/PET, PE/OBR/PP,        EVOH/OBR/PET, PE/OBR/COC.    -   Four-layer structure: PE/PET/OBR/PET, PE/OBR/EVOH/PET,        PET/OBR/EVOH/PET, PE/OBR/EVOH/COC.    -   Five-layer structure: PET/OBR/PET/OBR/PET, PE/PET/OBR/EVOH/PET,        PET/OBR/EVOH/COC/PET PET/OBR/PET/COC/PET, PE/OBR/EVOH/COC/PET.    -   Six-layer structure: PET/OBR/PET/OBR/EVOH/PET,        PE/PET/OBR/COC/EVOH/PET, PET/OBR/EVOH/PET/COC/PET    -   Seven-layer structure: PET/OBR/COC/PET/EVOH/OBR/PET.

In producing the above laminates, an adhesive resin may, as required, beinterposed among the resin layers.

As the adhesive resin, there can be exemplified a thermoplastic resincontaining carbonyl (—CO—) groups based upon carboxylic acid, carboxylicanhydride, carboxylate, carboxylic acid amide or carboxylic acid esterat a concentration of 1 to 700 milliequivalent (meq)/100 g of resin and,particularly, at a concentration of 10 to 500 meq/100 g of the resin onthe main chain or on the side chains. Preferred examples of the adhesiveresin include ethylene/acrylic acid copolymer, ionically crosslinkedolefin copolymer, maleic anhydride-grafted polyethylene, maleicanhydride-grafted polypropylene, acrylic acid-grafted polyolefin,ethylene/vinyl acetate copolymer, copolymerized polyester andcopolymerized thermoplastic resin, which may be used in one kind or in acombination of two or more kinds. These resins can be effectivelylaminated by the simultaneous extrusion or by the sandwich lamination.

Further, a thermosetting adhesive resin of the isocyanate type or theepoxy type can be used as the adhesive layer for adhering the gasbarrier resin film that has been formed in advance to themoisture-resistant resin film.

In the multi-layer structure of the present invention, though there isno particular limitation, it is desired that the thickness of the gasbarrier layer generally lies in a range of from 3 to 100 μm and,particularly, from 5 to 50 μm. That is, when the thickness of the gasbarrier layer becomes smaller than a given range, the gas barrierperformance becomes poor. Even when the thickness becomes larger thanthe given range, on the other hand, there is obtained no particularlydistinguished advantage in regard to the gas barrier property but ratherdisadvantage results concerning the economy such as an increase in theamount of resin and a decrease in the flexibility and softness of thematerial.

In the multi-layer structure of the present invention, it is desiredthat the entire thickness is generally from 30 to 7000 μm and,particularly, from 50 to 5000 μm though it may vary depending upon theuse. It is, on the other hand, desired that the oxygen barrierintermediate layer has a thickness which is from 0.5 to 95% and,particularly, from 1 to 50% of the entire thickness.

The multi-layer structure of the present invention can be produced by aknown method with the exception of using the gas barrier layer.

For example, the film, sheet or tube is formed by melt-kneading theabove resin composition by using an extruder and extruding it into apredetermined shape through a T-die or a circular die (ring die) therebyto obtain a T-die film, an inflation film or the like film. The T-diefilm is biaxially stretched to obtain a biaxially stretched film.

Further, the resin composition is melt-kneaded by using an injector, andis injected into an injection metal mold thereby to produce a containeror a preform for producing a container.

Further, the resin composition is extruded into a mass of a molten resinthrough the extruder and is compression-molded by using a metal mold toproduce a container or a preform for producing a container.

The molded article may assume the shape of a film, a sheet, a parison ora pipe for forming a bottle or a tube, and a preform for forming abottle or a tube.

The bottle is easily formed from the parison, pipe or preform bypinching-off the extruded article by using a pair of split molds, and byblowing a fluid therein.

After cooled, further, the pipe or the preform is heated at a drawingtemperature and is stretched in the axial direction and is furtherblow-stretched in the circumferential direction by utilizing the fluidpressure to obtain a draw-blown bottle or the like.

Further, the film or sheet is subjected to such means as vacuum molding,compressed air molding, inflation molding or plug assisted molding toobtain a packaging container in the shape of a cup or tray and a covermember formed of a film or a sheet.

The packaging material such as a film can be used as packaging bags of avariety of forms, and can be produced by a known bag-producing method.Examples of the bag include ordinary three-side sealed or four-sidesealed pouches, pouches with gusset, standing pouches andpillow-wrapping bags, to which only, however, the bags are in no waylimited.

The multi-layer extrusion molded article can be produced by using aknown co-extrusion molding method by using extruders of a numbercorresponding to the kinds of the resins, and by conducting theextrusion molding in the same manner as described above but using amulti-layer multiple die.

Further, the multi-layer injection molded article is produced relyingupon the co-injection method or the sequential injection method by usingthe injection molding machines of a number corresponding to the kind ofthe resins.

Further, the multi-layer film and the multi-layer sheet are producedrelying upon the extrusion coating method or the sandwich laminationmethod. Further, the multi-layer film or sheet can be produced bydry-laminating the films that have been formed in advance.

The multi-layer container of the present invention is useful forpreventing a drop of flavor of the content caused by oxygen.

The contents that can be contained may be such beverages as beer, wine,fruit juices, carbonated soft drinks, etc., such foods as fruits, nuts,vegetables, meet products, infant's foods, coffee, jam, mayonnaise,ketchup, edible oil, dressing, sauces, food boiled down in soy, milkproducts, etc., as well as medicines, cosmetics, gasoline, etc. that aresubject to be deteriorated in the presence of oxygen, though thecontents are in no way limited thereto only.

EXAMPLES

The present invention will now be described by way of Examples to whichonly, however, the invention is not limited.

[Measurement of Diameter of Dispersed Particles, Aspect Ratio of theDispersed Particles and Area Ratio Occupied by the Dispersed Particles]

A multi-layer structure cut from a multi-layer bottle, multi-layer cupor laminated film was buried in an epoxy/amine-type burying film forelectron microscope, and the burying resin was cured. Then, the buryingsample was polished by using a microtome (2050 SUPERCUT: Leica Co.) suchthat there appeared the cross section in the direction of thickness ofthe multi-layer structure (cross section in a direction perpendicular tothe direction of height when the multi-layer structure was a barrel of acontainer of the shape of a bottle or a cup, or cross section in adirection perpendicular to the drawing direction when the multi-layerstructure was a sheet or a film). Then, the burying sample was immersedin osmic acid a whole day to dye carbon-carbon double bond moiety of thepolyene polymer. The burying sample after dyed was finish-polished byusing an ultra-microtome (REIHERT URLTRACUTS: Leica Co.), and wasobserved by using a scanning-type electron microscope (JSM-6300F: NihonDenshi Co.) at a magnification of 3,000 to 20,000 times to take an SEMphotograph.

The picture of the SEM photograph was taken in by a scanner (GT-7600U:Seiko-Epson Co.). The polyene polymer moiety was distinguished fromother portions on a PC screen by using a picture processing software tothereby measure an area S of dispersed particles of the polyene polymerpresent on a predetermined area S_(o) and the number n of dispersedparticles. The operation was conducted for a plurality of visual fieldsto improve the precision, ΣS and Σn were calculated from S and n foundfrom the visual fields, and an area average particle diameter d wasfound in compliance with the following formula (1),d=(ΣS/Σn)^(1/2)  (1)

From S_(o) and S found from the plurality of visual fields, further, anarea ratio α occupied by the dispersed particles was found in compliancewith the following formula,α=100×ΣS/ΣS _(o)  (2)

Further, the above SEM photograph was enlarged, lines were drawn in adirection of thickness (short axis direction) of the gas barrier layerand in a direction (long axis direction) perpendicular thereto to find alength of the dispersed particles in the long axis direction and alength thereof in the short axis direction, to find an aspect ratio(length in the long axis direction/length in the short axis direction),and to obtain a maximum aspect ratio of the dispersed particles.

[Measurement of Acid Value]

The sample was completely dissolved in a suitable solvent and was, then,titrated with an alcoholic 0.1N KOH solution to find the total acidvalue of the sample.

[Measurement of the Number Average Molecular Weight]

The sample was dissolved in chloroform and was measured for its numberaverage molecular weight by using a gel permeation chromatography(column: TSK G5000HHR+4000HHR: Toso Co.) to which was connected adetection system (TriSEC 302TDA detector: Asahi Techneion Co.) equippedwith a light scattering detector, a refraction detector and a viscositydetector.

[Measurement of Oxygen Permeation Property of Multi-Layer Structure]

An oxygen permeability coefficient measuring apparatus (OX-TRAN 2/20:Modern Control Co.) was used. The following method was employed when thesample failed to possess the area of the transmission cell (circle of anarea of 50 cm²). A laminate obtained by sticking a biaxially stretchedpolyethylene terephthalate film of a thickness of 50 μm to an aluminumfoil of a thickness of 50 μm was cut into a square of a side of 10 cm,and a hole of a diameter of 25 or 50 mm was perforated in the center.The polyethylene terephthalate film of this laminate was peeled up tothe portion of the hole, and a sample to be measured was stuck with asticking agent so as to close the hole. At this moment, attention wasgiven to a sufficient degree so that no air bubble entered into betweenthe sample to be measured and the sticking agent. Then, the polyethyleneterephthalate film that was peeled was carefully placed thereon so thatno air bubble was entrapped therein thereby to prepare a holder havingthe sample to be measured being fitted in the hole. The holder wasmounted on the OX-TRAN, and the area of the sample to be measured wascorrected thereby to find the amount of oxygen that has permeatedthrough. The amount of oxygen that has permeated through was measured byflowing pure oxygen into the cell on one side and flowing a nitrogen gas(blended with 1% of a hydrogen gas) into another cell under atemperature-humidity condition of 30° C.-80% RH.

[Measurement of Oxygen Permeation Property of the Multi-Layer Container]

The interior of a vacuum gloved box was substituted with a nitrogen gas.Distilled water in an amount of 1 cc was introduced into the multi-layercontainer in the box, and the opening was heat-sealed with a closuremember for olefin having an aluminum foil as a barrier member. Thecontainer was boiled in a retort oven under a hydrothermal isobariccondition at 85° C. for 30 minutes and was, then, preserved in anatmosphere of 30° C.-80% RH. The amount of oxygen that has permeatedthrough after one day has passed was measured by using a gaschromatography (GC-3BT: Shimazu Seisakusho Co., detector: TCD (60° C.),column: Molecular Sieve 5A (100° C.), carrier gas: argon).

Example 1

Ethylene/vinyl alcohol copolymer resin pellets (EP-F101B: Kurare Co.)copolymerized with 32 mol % of ethylene and a cobalt neodecanoatecontaining 14% by weight of cobalt (DICNATE 5000: Dainihon Ink KagakuKogyo Co.) were mixed together in a tumbler, so that the cobaltneodecanoate was homogeneously deposited in an amount of 350 ppmcalculated as the amount of cobalt on the surfaces of the ethylene/vinylalcohol copolymer resin pellets.

Next, by using a biaxial extruder (TEM-35B: Toshiba Kikai Co.) having astrand die mounted on the outlet portion thereof, a maleicanhydride-modified liquid polybutadiene (M-2000-20: Nihon Sekiyu KagakuCo.) having a number average molecular weight of 5800 and an acid valueof 40 KOHmg/g was added dropwise by using a liquid feeder in an amountof 30 parts by weight per 970 parts by weight of the ethylene/vinylalcohol copolymer resin on which cobalt has been deposited whileevacuating to a low degree at a screw rotational speed of 100 rpm. Then,the strands were drawn at a molding temperature of 200° C. to preparepellets. The pellets had been blended with the maleic anhydride-modifiedpolybutadiene in an amount of 3% by weight.

By using the thus prepared pellets, a three-kind-five-layer parison(LDPE/adhesive/gas barrier layer/adhesive/LDPE) was extruded under theconditions of a shell diameter of 15 mm and a core diameter of 13 mm toprepare a wide-mouth multi-layer bottle of the shape of a jar having amouth diameter of 44 mm and a volume of 125 cc by the direct blowingmethod. The resins of the multi-layer bottle were so selected as topossess a weight ratio of LDPE of 92% by weight, adhesive of 4% byweight and gas barrier layer of 4% by weight. The thinnest portion ofthe multi-layer bottle possessed a thickness of 0.7 mm. The multi-layerstructure obtained by cutting the thinnest portion was measured for thediameter of the polyene polymer dispersed particles in cross section ofthe gas barrier layer in the direction of thickness to find an areaaverage particle diameter of 0.30 μm and an area ratio occupied by thedispersed particles of 3.5%. The amount of oxygen that has permeatedthrough the multi-layer structure was 0.2 cc/m²/day/atom manifestingexcellent barrier property.

Further, the multi-layer bottle was boiled, and the amount of oxygenpermeation one day after the boiling was measured. As a result, theamount of oxygen that has permeated was 0.02 cc per a bottle. Thus, themulti-layer structure of the invention exhibited excellent gas barrierproperty even after it was subjected to a severe processing such asboiling.

Example 2

Pellets were prepared in the same manner as in Example 1 with theexception of adding the maleic anhydride-modified liquid polybutadienedropwise in an amount of 50 parts by weight per 950 parts by weight ofthe ethylene/vinyl alcohol copolymer resin to which cobalt has beendeposited. The pellets had been blended with the maleicanhydride-modified polybutadiene in an amount of 5% by weight.

By using the thus prepared pellets, a three-kind-five-layer parison(PP/adhesive/gas barrier layer/adhesive/PP) was extruded under theconditions of a shell diameter of 15 mm and a core diameter of 13 mm toprepare a wide-mouth multi-layer bottle of the shape of a jar having amouth diameter of 44 mm and a volume of 125 cc by the direct blowingmethod. The resins of the multi-layer bottle were so selected as topossess a weight ratio of PP of 92% by weight, adhesive of 4% by weightand gas barrier layer of 4% by weight. The thinnest portion of themulti-layer bottle possessed a thickness of 0.7 mm. The multi-layerstructure obtained by cutting the thinnest portion was measured for thediameter of the polyene polymer dispersed particles in cross section ofthe gas barrier layer in the direction of thickness to find an areaaverage particle diameter of 0.28 μm and an area ratio occupied by thedispersed particles of 4.9%. The amount of oxygen that has permeatedthrough the multi-layer structure was 0.1 cc/m²/day/atom manifestingexcellent barrier property.

Further, the multi-layer bottle was boiled, and the amount of oxygenpermeation one day after the boiling was measured. As a result, theamount of oxygen that has permeated was 0.015 cc per a bottle. Thus, themulti-layer structure of the invention exhibited excellent gas barrierproperty even after it was subjected to a severe processing such asboiling.

Example 3

A three-kind-five-layer sheet (PP/adhesive/gas barrierlayer/adhesive/PP: 550 μm/20 μm/60 μm/20 μm/550 μm) was prepared byusing the pellets obtained in Example 2 as a gas barrier layer. By usingthis multi-layer sheet, a round-shaped cup having an H/D ratio(height/mouth diameter ratio) of 0.8 and a volume of 125 cc was formedby a solid-phase molding method. The thinnest portion of the cuppossessed a thickness of 0.36 mm. The multi-layer structure obtained bycutting the thinnest portion was measured for the diameter of thepolyene polymer dispersed particles in cross section of the gas barrierlayer in the direction of thickness to find an area average particlediameter of 0.27 μm and an area ratio occupied by the dispersedparticles of 5.1%. The amount of oxygen that has permeated through themulti-layer structure was 0.2 cc/m²/day/atom manifesting excellentbarrier property.

Further, the multi-layer cup was boiled, and the amount of oxygenpermeation one day after the boiling was measured. As a result, theamount of oxygen that has permeated was 0.004 cc per a cup. Thus, themulti-layer structure of the invention exhibited excellent gas barrierproperty even after it was subjected to a severe processing such asboiling.

Example 4

A multi-layer cup was prepared in the same manner as in Example 3 withthe exception of adding the maleic anhydride-modified liquidpolybutadiene dropwise in an amount of 10 parts by weight per 990 partsby weight of the ethylene/vinyl alcohol copolymer resin to which cobalthas been deposited. The thinnest portion of the cup possessed athickness of 0.36 mm. The multi-layer structure obtained by cutting thethinnest portion was measured for the diameter of the polyene polymerdispersed particles in cross section of the gas barrier layer in thedirection of thickness to find an area average particle diameter of 0.29μm and an area ratio occupied by the dispersed particles of 1.0%. Theamount of oxygen that has permeated through the multi-layer structurewas 1.1 cc/m²/day/atom manifesting excellent barrier property.

Further, the multi-layer cup was boiled, and the amount of oxygenpermeation one day after the boiling was measured. As a result, theamount of oxygen that has permeated was 0.02 cc per a cup. Thus, themulti-layer structure of the invention exhibited excellent gas barrierproperty even after it was subjected to a severe processing such asboiling.

Example 5

A three-kind-five-layer sheet (PP/adhesive/gas barrierlayer/adhesive/PP: 280 μm/10 μm/20 μm/10 μm/280 μm) having a thicknessof 0.6 mm was prepared by using the pellets obtained in Example 1 as agas barrier layer. The multi-layer sheet was cut out and was measuredfor the diameter of the polyene polymer dispersed particles in crosssection in the direction of thickness, i.e., in a directionperpendicular to the direction of drawing to find an area averageparticle diameter of 0.21 μm and an area ratio occupied by the dispersedparticles of 3.1%. A maximum aspect ratio of the dispersed particles was1.1.

The amount of oxygen that has permeated through the multi-layerstructure was 0.2 cc/m²/day/atom manifesting good barrier property.

Example 6

A three-kind-five-layer sheet (PP/adhesive/gas barrierlayer/adhesive/PP: 390 μm/16 μm/23 μm/16 μm/390 μm) having a thicknessof 0.84 mm was prepared by using the pellets obtained in Example 1 as agas barrier layer. The multi-layer sheet was stretched in a directionperpendicular to the direction of drawing to obtain a sheet having athickness of 0.6 mm. A portion which was evenly stretched was cut outfrom the sheet and was measured for the diameter of the polyene polymerdispersed particles in cross section in the direction of stretch to findan area average particle diameter of 0.21 μm and an area ratio occupiedby the dispersed particles of 3.0%. A maximum aspect ratio of thedispersed particles was 2.0.

The amount of oxygen that has permeated through the multi-layerstructure was 0.1 cc/m²/day/atom. Upon increasing the aspect ratio,there was obtained a multi-layer sheet having a barrier propertyincreased to be higher than that of Example 5.

Example 7

A maleic anhydride-modified liquid polybutadiene having a number averagemolecular weight of 6300 and an acid value of 20 KOHmg/g was prepared.By using this resin, a multi-layer bottle was prepared in the samemanner as in Example 1. The multi-layer structure was obtained bycutting out the thinnest portion of the multi-layer bottle and wasmeasured for the diameter of the polyene polymer dispersed particles incross section of the gas barrier layer in the direction of thickness tofind an area average particle diameter of 1.0 μm and an area ratiooccupied by the dispersed particles of 3.3%. The amount of oxygen thathas permeated through the multi-layer structure was 0.4 cc/m²/day/atommanifesting excellent barrier property.

Further, the multi-layer bottle was boiled, and the amount of oxygenpermeation one day after the boiling was measured. As a result, theamount of oxygen that has permeated was 0.06 cc per a bottle. Thus, themulti-layer structure of the invention exhibited excellent gas barrierproperty even after it was subjected to a severe processing such asboiling.

Comparative Examples 1 to 3

Multi-layer structures were prepared under the same conditions as thoseof Examples 1, 3 and 5 by using, as a gas barrier layer, anethylene/vinyl alcohol copolymer resin containing neither the polyenepolymer nor the transition metal catalyst, and the amounts of oxygenpermeation were measured. As a result, the amounts of oxygen that haspermeated through the multi-layer structures obtained from a multi-layerbottle, a multi-layer cup and a multi-layer sheet were 4.1cc/m²/day/atm, 4.8 cc/m²/day/atm and 5.0 cc/m²/day/atm. Thus, thebarrier properties were inferior by more than 10 times to those of themulti-layer structures having a gas barrier layer blended with thepolyene polymers of Examples 1, 3 and 5.

Comparative Example 4

A multi-layer bottle was prepared under the same conditions as those ofExample 2 by using, as a gas barrier layer, an ethylene/vinyl alcoholcopolymer resin containing neither the polyene polymer nor thetransition metal catalyst, and a multi-layer structure was obtained inthe same manner as in Example 2. The amount of oxygen that has permeatedthrough the multi-layer structure was 4.0 cc/m²/day/atm. Thus, thebarrier property was inferior by more than 10 times to that of themulti-layer structure of Example 2.

Further, the multi-layer bottle was boiled, and the amount of oxygenpermeation one day after the boiling was measured. As a result, theamount of oxygen that has permeated was 0.26 cc per a bottle. Thus, theoxygen barrier property under the wet heated condition was very inferiorto that of the multi-layer bottle of Example 2.

Comparative Example 5

A multi-layer bottle was prepared in the same manner as in Example 1with the exception of blending 993 parts by weight of the ethylene/vinylalcohol copolymer resin with 7 parts by weight of a maleicanhydride-modified liquid polybutadiene (M-2000-20: Nihon Sekiyu KagakuCo.). A multi-layer structure was obtained by cutting out the thinnestportion of the multi-layer bottle in the same manner as in Example 1 andwas measured for the diameter of the polyene polymer dispersed particlesin cross section of the gas barrier layer in the direction of thicknessto find an area average particle diameter of 0.29 μm and an area ratiooccupied by the dispersed particles of 0.7%. The amount of oxygen thathas permeated through the multi-layer structure was 2.3 cc/m²/day/atmmanifesting poor barrier property.

Comparative Example 6

A multi-layer bottle was prepared in the same manner as in Example 1with the exception of using a polybutadiene (B-2000: Nihon Sekiyu KagakuCo.) instead of using the maleic anhydride-modified liquidpolybutadiene. The obtained multi-layer bottle exhibited very rough skindue to defective molding of the gas barrier layer, and exhibited verypoor appearance.

A multi-layer structure was obtained by cutting out the thinnest portionof the multi-layer bottle in the same manner as in Example 1 and wasmeasured for the diameter of the polyene polymer dispersed particles incross section of the gas barrier layer in the direction of thickness tofind an area average particle diameter of 1.5 μm and an area ratiooccupied by the dispersed particles of 1.5%.

Comparative Example 7

A multi-layer bottle was prepared in the same manner as in Example 1with the exception of using a terminal hydroxyl group-modifiedpolyioprene (Poly ip: Idemitsu Sekiyu Kagaku Co.) instead of using themaleic anhydride-modified liquid polybutadiene. In this case, too, thebottle exhibited very rough skin and a very poor appearance like inComparative Example 6. A multi-layer structure was obtained by cuttingout the thinnest portion of the multi-layer bottle in the same manner asin Example 1 and was measured for the diameter of the polyene polymerdispersed particles in cross section of the gas barrier layer in thedirection of thickness to find an area average particle diameter of 2.3μm and an area ratio occupied by the dispersed particles of 1.8%.

The above results are summarized in Table 1. TABLE 1 Oxydizing organiccomponent Area Average Number average acid average Blending particle Ex.& value molecular amount size Comp. Ex. Kind (KOHmg/g) weight (wt %)Molded article (μm) Ex. 1 maleic anhydride- 40 5800 3 multi-layer bottle0.30 modified polybutadiene Ex. 2 maleic anhydride- 40 5800 5multi-layer bottle 0.28 modified polybutadiene Ex. 3 maleic anhydride-40 5800 5 multi-layer cup 0.27 modified polybutadiene Ex. 4 maleicanhydride- 40 5800 1 multi-layer cup 0.29 modified polybutadiene Ex. 5maleic anhydride- 40 5800 3 multi-layer sheet 0.21 modifiedpolybutadiene Ex. 6 maleic anhydride- 40 5800 3 multi-layer sheet 0.21modified polybutadiene Ex. 7 maleic anhydride- 20 6300 3 multi-layerbottle 1.0  modified polybutadiene Comp. Ex. 1 — — — — multi-layerbottle — Comp. Ex. 2 — — — — multi-layer cup — Comp. Ex. 3 — — — —multi-layer sheet — Comp. Ex. 4 — — — — multi-layer bottle — Comp. Ex. 5maleic anhydride- 40 5800 0.7 multi-layer bottle 0.29 modifiedpolybutadiene Comp. Ex. 6 polybutadinene — could not 3 multi-layerbottle 1.5  be measured Comp. Ex. 7 terminal OH- — could not 3multi-layer bottle 2.3  modified be measured Polyisoprene O₂ permeationO₂ permeation amount thru amount thru Area Max. aspect multi-layermulti-layer Ex. & ratio ratio of structure container Comp. Ex. (%)particles (cc/m²/day/atm) (cc/container) Remarks Ex. 1 3.5 could not 0.20.02  good barrier property be measured Ex. 2 4.9 could not 0.1 0.015 ″be measured Ex. 3 5.1 could not 0.2 0.004 ″ be measured Ex. 4 1.0 couldnot 1.1 0.02  ″ be measured Ex. 5 3.1 1.1 0.2 — ″ Ex. 6 3.0 2 0.1 — Maxaspect is 2 or greater and barrier property is superior to Ex. 5 Ex. 73.3 could not 0.4 0.06  good barrier property be measured Comp. Ex. 1 —— 4.1 could not be O₂ permeation is 10 or more times as measured greatas Ex. 1. Comp. Ex. 2 — — 4.8 could not be O₂ permeation is 10 or moretimes as measured great as Ex. 3. Comp. Ex. 3 — — 5.0 — O₂ permeation is10 or more times as great as Ex. 5. Comp. Ex. 4 — — 4.0 0.26  O₂permeation is 10 or more times as great as Ex. 2. Comp. Ex. 5 0.7 couldnot 2.3 could not be O₂ permeation is 10 or more times as be measuredmeasured great as Ex. 1. Comp. Ex. 6 1.5 could not could not be couldnot be Dispersed particles are so coarse be measured measured measuredthat molded bottle exhibits roush skin and poor appearance Comp. Ex. 71.8 could not could not be could not be Dispersed particles are socoarse be measured measured measured that molded bottle exhibits roushskin and poor appearance

According to the present invention, a gas barrier layer is formed byblending a particular gas barrier resin with a transition metal catalystand an oxidizing organic component, and the dispersion structure and theprofile structure of the oxidizing organic component are controlled tolie within particular ranges in cross section of the gas barrier layerin the direction of thickness thereof. Then, it is allowed to markedlyimprove the oxygen permeation coefficient of the multi-layer structureunder the wet heated condition while maintaining excellent workabilityand mechanical strength.

1. A multi-layer structure having a gas barrier layer with excellent gasbarrier property, said gas barrier layer comprising a resin compositionobtained by blending a thermoplastic resin having an oxygen permeationcoefficient at 20° C. and 0% RH of not larger than 10⁻¹²cc·cm/cm²/sec/cmHg with a transition metal catalyst and an oxidizingorganic component, said oxidizing organic component having an averagediameter of dispersed particles of not larger than 1 μm as found by anarea method in cross section of said gas barrier layer in the directionof thickness thereof, and an area ratio occupied by the dispersedparticles being not smaller that 1% in cross section of said gas barrierlayer in the direction of thickness thereof.
 2. A multi-layer structureaccording to claim 1, wherein when the direction of thickness of saidgas barrier layer is regarded to be a short axis and a directionperpendicular to the direction of thickness is regarded to be a longaxis in cross section of said gas barrier layer in the direction ofthickness thereof, a maximum value of an aspect ratio of dispersedparticles of said oxidizing organic component represented by the lengthin the long axis direction/length in the short axis direction, is notsmaller than
 2. 3. A multi-layer structure according to claim 2, whereinsaid oxidizing organic component is a polyene polymer.
 4. A multi-layerstructure according to claim 3, wherein said oxidizing organic componentis a resin having a functional group.
 5. A multi-layer structureaccording to claim 4, wherein said oxidizing organic component is aresin having a carboxylic acid group or a carboxylic anhydride group. 6.A multi-layer structure according to claim 5, wherein said thermoplasticresin is an ethylene/vinyl alcohol copolymer.
 7. A multi-layer structureaccording to claim 1, wherein said oxidizing organic component is apolyene polymer.
 8. A multi-layer structure according to claim 7,wherein said oxidizing organic component is a resin having a functionalgroup.
 9. A multi-layer structure according to claim 8, wherein saidoxidizing organic component is a resin having a carboxylic acid group ora carboxylic anhydride group.
 10. A multi-layer structure according toclaim 9, wherein said thermoplastic resin is an ethylene/vinyl alcoholcopolymer.
 11. A multi-layer structure according to claim 1, whereinsaid oxidizing organic component is a resin having a functional group.12. A multi-layer structure according to claim 1, wherein said oxidizingorganic component is a resin having a carboxylic acid group or acarboxylic anhydride group.
 13. A multi-layer structure according toclaim 1, wherein said thermoplastic resin is an ethylene/vinyl alcoholcopolymer.
 14. A multi-layer structure according to claim 2, whereinsaid oxidizing organic component is a resin having a functional group.15. A multi-layer structure according to claim 2, wherein said oxidizingorganic component is a resin having a carboxylic acid group or acarboxylic anhydride group.
 16. A multi-layer structure according toclaim 2, wherein said thermoplastic resin is an ethylene/vinyl alcoholcopolymer.